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This invention relates to bacteriostatic agents and more particularly to synthetic detergent additives which have bacteriostatic properties and which are substantive to cotton fabrics washed in an aqueous solution containing at least one of the agents and a synthetic detergent.

The bacteriostatic agents of this invention are metal salts of 2,2-thiobis (4,6-dichloropheno1), also called bithionol. The parent compound has been recognized as a bacteriostatic agent for some time. While the parent compound has been reported to be effective against all of the gram-positive bacteria and frequently effective against gram-negative species, it has not been found to be particularly effective against some of the more common types of fungi.

However, it has been found that the parent compound has decided limitations on its uses. For example, one

extremely important use of such bacteriostatic agents is to impart bacteriostatic properties to fabrics and especially to cotton fabrics such as denim or duck. If a bacteriostat effective against the gram-positive bacteria, and more specifically the cocci that comprises a large proportion of the normal resident bacterial flora of the skin, is sufficiently substantive to cotton so as to withstand washing, it will, if incorporated in the Washing solution, remain behind on the fabric and prevent multiplication of such bacteria and the development, on the fabric, of body odors. While substantivity of bithionol itself to the skin has been recognized, resulting in its incorporation in soaps, and while the parent compound so incorporated has been found to be cotton substantive, it has been ob served that this cotton substantivity is not manifested by bithionol incorporated in a synthetic detergent. Since cotton fabrics are ordinarily washed in washing machines with synthetic detergents, this lack of substantivity renders the compound unsatisfactory as an additive for synthetic detergents.

It has now been found that in surprising contrast to the non-substantivity of bithionol itself, metal salts of the parent compound are substantive to cotton fabrics washed in aqueous solutions of a mixture of detergents and the salts. While these salts are effective in concentrations as low as 0.1% by weight based on the detergent, we prefer to use them in concentrations of at least about 0.5%.

When reference is made herein to synthetic detergents or detergents it should be considered to mean any combination of a synthetic surfactant with a phosphate and/ or mixed phosphates. Surfactants are substances which alter the conditions prevailing at interfaces and synthetic surfactants are substances which have been specially synthesizbd in order to obtain surface-active effects. Such surfactants should be understood to include the anionic, cationic, non-ionic or amphoteric surfactant types.

An object of this invention is to provide a method for imparting bacteriostatic properties to a cotton fabric which includes washing the fabric in an aqueous solution of a synthetic detergent as defined above which has included therein a metal salt derivative of 2,2'-thiobis (4,6-dichlorophenol).

Another object is to provide a cotton fabric having bacteriostatic properties which has substantively distributed thereon a small amount of a metallic salt of 2,2-

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amass Patented Mar. 6, 1

on oc1Os-@or where M is selected from the group consisting of H, Na, K and Li, M is selected from the group consisting of Na, K and Li, and M" is selected from the group consisting of Zn and Ca.

Other objects and features will become more apparent from the description which follows below.

When reference is made herein to cotton fabric or cotton any fabric which includes cotton as one of the fibers is meant to be included. Reference made herein to a material being substantive or the substantivity of a material refers to the fact that the material adheres to the fibers when they have been Washed in a solution containing the material, even after rinsing said washed fibers.

Most of the metallic salts of the compound 2,2'-thiobis (4,6-dichlorophenol) were prepared by first forming the sodium salt of the parent compound by adding the theoretical amount of sodium hydroxide in solution, following which soluble salts of the various cations were added and the resulting precipitates collected, washed, dried and tested. The salts prepared in this Way included the sodium, lithium, strontium, calcium, barium, magnesium, zinc, bismuth, chromium, cobalt, cadmium, cuprous, ferric and lead salts. The potassium salt was prepared by treating the parent compound with potassium hydroxide and the resulting solution which contained a small quantity of precipitate was used without isolation in preparing the test media. The tellurium derivative was prepared from sodium tellurite and the sodium salt of the parent compound, adding sulfuric acid to precipitate the White tellurium salt.

In order to test the bacteriostatic properties and cotton substantivity of the parent compound and its salts, a standard biological test for cotton substantivity was employed. The results of these tests are set out below in tables.

Table I shows a basic screening of all of the metallic salts of bithionol as compared to results obtained using the parent compound.

Table II shows the results of tests using mixtures of various kinds of synthetic detergents.

Table III shows the effect of various concentrations of the calcium salt and the effect of age on the detergentsalt mixture.

Table IV shows the effect of varying the ratios of phosphate or surfactant mixtures of detergents and two of the derivative salts.

Table V shows the effect of mixtures containing 1% by weight of a salt and the surfactant alone, mixed phosphates alone and the detergent containing both the surfactant and the mixed phosphates.

Table VI shows the effect of the addition of caustic soda to the detergent-bithionol mixture and detergentderivative salt mixture.

The biological testing procedure made use of the cotton substantivity test given below unless otherwise indicated.

COTTON SUBSTANTIVITY TEST The cotton substantivity screening of the various salts was performed according to the following procedure. Into an 800 milliliter beaker equipped with an electric stirrer, there was placed 499 ml. of tap water (usually at 120 F. to correspond with the normal washing temperature for home laundries) and 1 gram of a synthetic detergent having a composition as follows:

40% Ultrawet K (a commercial alkyl aryl sulfonate surfactant of the anionic type) 15% sodium hexametaphosphate 15% sodium tripolyphosphate 15% sodium tetraphosphate 15% trisodium phosphate (The mixture of the four phosphates will be referred to hereinafter as mixed phosphates) The detergent contained the specified percent by weight of a test chemical either blended in the dry detergent prior to its addition to the beaker or added in solution to the aqueous solution of the detergent. For example 0.01 gram of the test chemical added to the water containing one gram of the detergent achieves a 1% test compound based on the weight of the detergent.

The solution of water, detergent and test chemical is agitated for a short period of time. Following the preparation of the washing solution the fabric samples are added. Usually about six sample are washed at a time. One inch diameter circles or one inch square pieces of 8 oz. bleached cotton duck or other fabric are employed as fabric samples.

The fabric samples are agitated gently for 10 minutes in the test solution. All of the fabric samples are then removed and half of them thoroughly rinsed in 125 milliliters of tap water for a period of 2 minutes. Both the washed and the rinsed samples are allowed to air dry.

Sterile, melted and cooled nutrient agar is inoculated with respective selected test organisms by adding an 18 hour nutrient broth culture of each test organism, which has had three consecutive daily transfers through nutrient broth, to the sterile agar. The inoculation concentration is 10 ml. of broth culture per 500 ml. of agar. The inoculated agar is then poured into sterile Petri dishes and allowed to harden. These cultures are normally prepared in advance so as to be ready for use when the fabric samples have been prepared.

The dried, washed and rinsed samples (identified in the tables below by the letters W for washed and R for rinsed) are placed on the inoculated agar and incubated at 37 012 C. for 18 to 24 hours. Fabric samples containing thereon effective quantities of bacteriostat exhibit a zone of inhibition comprising an area surrounding the samples where bacterial growth was not observed.

The average diameter of the zone of inhibition is calculated for each test organism and sample. This is done by measuring the total diameter of the clear Zone of inhibition and subtracting the diameter of the sample. In instances where there was a zone of inhibition which was irregular and touched the fabric in some places these results have been shown below by the letters tr.

The test organisms employed are Bacillus subtilis, Staphylococcus aureus (antibiotic resistant, coagulasepositive, hemolytic strain) and Salmonella typhosa. These organisms were selected as representative of the major groups of bacteria and include two gram-positive, one gram-negative, one coccus, two rods, two pathogens and one spore-former.

Table I below sets forth the results of the basic screening of the various salts as compared with the parent compound using the above Cotton Substantivity Test. The larger the diameter of the zone of inhibition, the more effective the compound, due to its greater substantivity to the test sample.

Table l.-Substantivity 0f 2,2'-Thi0bis (4,6-Dichl0r0- phenol) and Its Salts to Cotton. Applied in 0.2% Aqueous Solution of Detergent at 120 F. (Unless Otherwise Specified). Test Compound at 1% Based on Weight of Detergent Diameter of zone of bacterial inhibition in mm.

Salt Color B. subtllts S. aureus Salm.

typhosa W R W R W R Bithionol 0 0 0 0 0 0 Sodium 4 2 4 2 2 2 Zine 5 4 3 1 3 1 Potassium Tr. Tr. Tr. 1 0 0 Calcium g g g g g g o 2 1 1 2 2 1 Tests at 8 7 7 5 2 2 Lithium 6 8 4 4 7 6 Tests at 80" 4 3 2 2 3 3 Strontium Tr. Tr. 2 1 Tr. 0 Bismuth YeL-green..- 1 1 Tr. Tr. Tr. Tr. Barium. White. Tr. Tr. 1 1 0 0 Chromium. 1 1 4 1 Tr. Tr. Cobalt 1 Tr. 2 1 Tr. 0 Magn sium Whit 3 Tr. 2 1 0 0 Manganese 2 l 4 3 3 Tr. Cadmium Vi 1 0 Tr. Tr. Tr. 0 Tr. Tr. 1 1 1 0 Tr. Tr. Tr. Tr. 0 0 Tr. Tr. 1 Tr. O 0 O 0 Tr. Tr. 0 0

Legend: W=washcd; R=washed and rinsed. All samples dried before testing.

It will be noted that all of the salts are superior to the parent compound against one or more of the three types of bacteria used in the tests. The sodium, zinc, calcium and lithium derivatives show outstanding substantivity with respect to all three of the types of cultures. The other derivatives all exhibit substantivity against the Staphyloccocus aureus, at least.

Table I lists the colors of the various salts. A white color is generally preferable for an additive for a synthetic detergent.

Certain of the salts are insoluble in water and therefore it is necessary to incorporate them in the dry detergent by thorough blending. However, the sodium, potassium and lithium salts are soluble and therefore can be used in liquid detergents. The calcium and lithium salts were used in a test washing solution at 80 F. in order to test the substantivity of the derivatives at the temperature to which the water may fall at the end of the wash cycle as compared to the F. at the beginning of the wash cycle of the home laundry. As the results show these salts retain their substantivity in such solutions.

The surfactant of the detergent used above is of the anionic type. In order to test the effectiveness of the bacteriostatic agent in other types of synthetic detergents,

non-ionic, cationic and amphoteric surfactant containing detergents were also tested. The results of these tests are set forth below in Tables IIA, B, C, D and E. Tables IIA, B and C employ one commercially available detergent and two commercially available surfactants representing these three types of surfactants. Tables IID and IIE show the results using laboratory test detergents containing 40% of the above commercial surfactant plus 60% of the mixed phosphates referred to above in the Cotton Substantivity Test. Since the sodium, zinc, calcium and lithium derivatives appeared to be the most effective from the basic screening of Table I, these four were used in the tests, the results of which are given in Tables IIA, IIB, IIC, IID and HE.

6 the commercially available surfactants used for Tables HA, IIB and 11C are employed per se.

In order to test the effect of varying the concentration of bithionol salt in the detergent, and the age of the mixture, upon cotton substantivity, detergent mixtures were prepared by blending varying amounts of the calcium derivative of bithionol with the mixed phosphates de scribed in the Cotton substantivity Test above. Tests were performed using freshly-prepared detergent-bithionol derivative mixtures and detergent-bithionol derivative mixtures which had been stored at room temperature in the dry state for three months. They were used in 0.2% aqueous solutions at 120 F. as described in the Cotton substantivity Test. Results of these tests are shown in Table HI.

Table II.-Substantivity of 2,2'-Thiobis (4,6-Dichloro- Table phenol) Salts 0n Cotton, Applied in 0.2% Aqueous SolutiOns 0f Detergent Containing 1% Of the Salts 1Concetntra- Diameter of zone of bacterial inhibiion 0 ca tion in mm. Based on the Weight of the Detergent salt percent A. ALU (NON-IONIC SURFACTANT CONTAINING Detergent by weight B. sabtilzs S. aureus Salm.

. SYNTHETIC DETERGENT) of detertyphosa gent) Diameter of zone of bacterial inhibition in mm. W R W R W 13.

Salt B. subtilis S. aureus Salm. typhosa 1.0 6 5 6 6 7 7 0. 75 4 2 3 3 2 T1. 0. 5 3 1 3 l 1 TI. W R R W R 1.0 5 2 6 4 4 3 0. 75 3 2 4 3 3 3 0. 5 2 2 3 2 2 2 Bithionol 0 0 0 0 0 0 Sodium 9 8 5 4 8 6 Zinc 3 3 1 Tr. s a Calcium 6 5 3 2 4 2 It w1ll be noted from Table III that the test compounds Lithium 3 3 1 Tr. 2 2

B. INTRACOL 0A (CATIONIO LONG CHAIN FATTY ACID AMIDE SURFACTANT) 0 0 0 0 0 0 7 6 3 2 6 4 0 O 0 O 0 0 5 4 1 Tr 3 2 5 5 1 1 4 2 C. ANTARCAIgfiFC 34" 1\(iXMPHOTERIC COMPLEX FATTY D. INTRACOL 0A (40% CATIONIC LONG CHAIN FATTY SURFACTANT PLUS 60% MIXED PHOS- Tr. 0 Tr. T1. 0 0 8 7 4 3 5 3 6 4 6 4 5 4 6 5 2 2 4 3 5 5 3 2 5 3 E. ANTARON FC 34 (40% AMPHOTERIC COMPLEX FATTY AMIDO COMPOUND SURFACTANT PLUS 60% MIXED PHOSPHATES) Bithionol T T Lithium:

are effective to some degree in concentrations as low as 0.5% based on the weight of the detergent and that the age of the mixture does not materially decrease the effectiveness.

Table IV sets forth the results of tests in which detergent mixtures containing varying ratios of phosphates to surfactants were employed. The detergent mixtures were as follows:

Detergent Mixtures (parts by weight) Sodium salt 1 1 1 Calcium salt. 1 1 1 The various detergent mixtures, identified by number, were used in the Cotton substantivity Test procedure described above.

Table IV Diameter of zone of bacterial inhibition in mm.

Test compound B. subtilis S. aureus -Salm. typhosa.

W R W R W R Table V contains the results of tests in which mixtures containing 1% by weight of the calcium derivative with either the anionic surfactant Ultrawet K alone, mixed phosphates alone, or the combined anionic surfactant and mixed phosphates were used.

The results shown in Table V indicate that the mixture of the calcium derivative salt and the anionic surfactant employed exhibits a high degree of cotton substantivity. The mixed phosphates-calcium derivative also shows good results although it is slightly less effective than the surfactant-derivative salt alone. The mixture of the surfactant and mixed phosphates plus the calcium derivative salts shows excellent results. These results indicate that it is possible to employ mixtures of either the anionic surfactant and derivative salt alone or the mixed phosphates-derivative salt mixture in washing solutions in order to impart bacteriostatic properties to cotton fabrics, and that netiher the mixed phosphates nor the surfactant have an appreciable effect on the Substantivity of the salts.

In order to determine whether the presence of caustic soda or sodium hydroxide affects the Substantivity of the parent compound or its calcium derivative, the Cotton Substantivity Test was run using mixtures of the following test solutions.

Make-up of test solutions Test compound Deter- NaOH, Water, gent, g. g. ml.

Bithionol 0.01 g 1. 0. 01 499 Calcium salt 0.01 g 1.0 0.01 499 The detergent used in the test solutions is the one described in the Cotton Substantivity Test. The results of these tests are set out in Table VI.

It will be noted that the presence of caustic soda does not increase the eifectiveness of the parent compound or afiect significantly the efficacy of the calcium derivative.

The above tests show that metallic salts of 2,2-thiobis (4,6-dichlorophenol), or bithionol, are substantive to cotton washed in a solution containing said salt together with any of the various types of synthetic detergents. Comparative tests using the parent compound in the same detergents and run' under the same conditions show that bithionol itself is not substantive to cotton. The contrast is truly surprising and most unexpected. The substantivity of the metallic salts of bithionol is not decreased appreciably by varying the proportions of phosphate builders present, by the presence of caustic alkali, nor by storage of the dry mixture for three months. Further tests show that the bithionol salts are effective when used in soap solutions, deodorants, sanitizing agents, and in cutting oils.

Other uses of the salts will be apparent to those skilled in the art and therefore the above should be considered as illustrative only of the uses to which the derivatives may be put. Therefore such other uses as are suggested by the above are within the spirit of this invention and the scope of the appended claims.

We claim:

1. A method of imparting bacteriostatic properties to a cotton fabric which comprises washing said fabric in an aqueous solution of a synthetic detergent having incorporated therewith at least about 0.5% by weight, based on the detergent, of a metal salt of 2,2-thiobis (4,6-dichlorophenol) and said metal being selected from the group consisting of calcium, lithium, sodium and zinc.

2. The method of claim 1 in which the said detergent is present in the said aqueous solution in a concentration of at least about 0.2% by weight.

3. The method of claim 1 in which the said metal is calcium.

4. The method of claim 1 in which the said metal is zinc.

5. A method of imparting bacteriostatic properties to a cotton fabric which comprises washing said fabric in an aqueous solution of a synthetic detergent having incorporated therewith at least 0.1% by weight, based on the detergent, of a metal salt of 2,2'-thiobis (4,6-dichlorophenol) and said metal being selected from the group consisting of calcium, lithium, sodium and zinc.

6. The method of claim 5 in which said detergent is present in an aqueous solution in a concentration of at least about 0.2% by weight.

7. The method of claim 5 in which the said metal is calcium.

8. The method of claim 5 in which the said metal is zinc.

9. The method of claim 5 in which the said metal is sodium.

10. The method of claim 5 in which the said metal is lithium.

11. A cotton fabric having substantively distributed thereon a metal salt of 2,2-thiobis (4,6-dichlorophenol), said metal being selected from the group consisting of calcium, lithium, sodium and zinc.

References Cited in the file of this patent UNITED STATES PATENTS 2,353,735 Kunz July 18, 1944 2,695,317 Cutler Nov. 23, 1954 2,897,235 Kosmin July 28, 1959 2,898,264 Weber Aug. 4, 1959 FOREIGN PATENTS 776,173 Great Britain June 5, 1957 

1. A METHOD OF IMPARTING BACTERIOSTATIC PROPERTIES TO A COTTON FABRIC WHICH COMPRISES WASHING SAID FABRIC IN AN ACQUEOUS SOLUTION OF A SYNTHETIC DETERGENT HAVING INCORPORATED THEREWITH AT LEAST ABOUT 0.5% BY WEIGHT, BASED ON THE DETERGENT, OF A METAL SALT OF 2,2''-THIOBIS (4,6-DICHLOROPHENOL) AND SAID METAL BEING SELECTED FROM THE GROUP CONSISTING OF CALCIUM, LITHIUM, SODIUM AND ZINC. 